In the industrial production of scalded-emulsion sausage and cooked-meat sausage, in addition to cellulose fiber casings, multilayer biaxially oriented plastic casings based on polyamide (PA) and in combination with other plastics have proved themselves in many aspects for years.
Biaxial orientation is understood by those skilled in the art to be transverse and longitudinal stretching of the thermoplastic extrudate at temperatures between the glass transition temperature and melting temperature of the polymeric materials. Biaxial orientation is customarily performed using a bubble filled with a gas or fluid pressure cushion, which bubble is enclosed gas-tightly or fluid-tightly between two roller pairs running at different speeds. During the stretching the molecules of the film tube in the solid state orientate themselves in such a manner that the modulus of elasticity and the strengths both in the transverse and in the longitudinal directions are increased to a considerable extent. Following the stretching there usually follows a further temperature treatment.
DE-A 43 39 337 describes a five-layer biaxially oriented tubular film for packaging and encasing foods. This casing is characterized in that it is made up of an inner and outer layer made of the same polyamide material and a middle polyolefin layer and also two bonding agent layers consisting of the same material.
EP-A 530 538 describes a five-layer coextruded biaxially oriented tubular film having at least three polyamide layers, polymer layers of water-barrier and oxygen-barrier character being incorporated between the inner and outer polyamide layers.
DE-A 198 18 358, for example, discloses spraying synthetic casings from the inside with a wax which acts at ambient temperature as bonding agent between the casing inner surface and the smoke concentrate, and a smoke concentrate, before shirring, in one operation. When the sausages are scalded, the wax is intended to give up its bonding agent function and thus release the smoke concentrate for transfer into the sausage meat emulsion mixture. The disadvantage of this process is the reproducibility of the process which is difficult to establish and the additional use of waxes for the sausage industry.
EP-A 0 884 951 describes a process in which a smoke concentrate is applied with a liquid coating to the inside of the film used not until just before, or during, the packaging of food, in particular sausage. A disadvantage here is considered to be the uneven amount of smoke concentrate applied.
For the meat-processing industry, it is of particular interest to process, for example, the abovementioned tubular casings with high efficiency. For this reason, the tubular casings are typically subjected to a shirring process in which, using a shirring mandrel, they are laid into pleats to form a shirred stick, so that the length of the shirred stick is drastically reduced. The shirring of tubular materials is known, as described in, for example, DE-A 8 944 623 C2.
The flexibility of polyamide casings in the dry state is not sufficient for product stuffing without creasing, in order still, after the cooking or scalding process, to deliver sufficient shrink properties of the casing so that a smooth crease-free sausage is formed.
For this reason, the polyamide-containing tube, shortly before stuffing with meat or with sausage, is immersed and/or watered in cold and also hot water. This procedure is described, inter alia, in DE-A 3 426 723.
According to the prior art described herein, production of smoke-impregnated, ready-to-stuff conditioned multilayer plastic casings is burdened with disadvantages.